Nickel-copper alloy

ABSTRACT

AN AGE HARDENABLE NICKEL-COPPER ALLOY HAVING MARKEDLY IMPROVED WELDABILITY AND MACHINABILITY WHICH ALLOY CONTAINS NOT MORE THAN ABOUT 0.1% CARBON, NOT MORE THAN ABOUT 0.5% TITANIUM, ABOUT 2.5% TO ABOUT 3.5% ALUMINUM, ABOUT 63% TO ABOUT 70% NICKEL AND THE BALANCE, EXCEPT FOR INCIDENTAL ELEMENTS AND IMPURITIES, ESSENTIALLY COPPER.

United States Patent O 3,578,440 NICKEL-COPPER ALLOY Herbert L.Eiselstein and flat! B. Haeberle, Huntington,

W. Va., assignors to The International Nickel Company, Inc., New York,NY.

Filed Mar. 25, 1968, Ser. No. 715,898 Int. Cl. C22c 19/00 US. Cl. 75-170Claims ABSTRACT OF THE DISCLOSURE Age hardenable nickel-copper alloyshave been known for many years and one such alloy, which nominallycontains about 0.15% carbon, about 0.25% to about 1% titanium, about 2%to about 4% aluminum, about 63% to about 70% nickel and the balance,except for incidental elements and impurities, essentially copper, hashad a long history of successful industrial use. The alloy is stronglyage hardenable by a heat treatment in the neighborhood of 1100 F. It isstrong, tough and ductible, is characterized by retention of strengthand ductility to very low temperatures and has excellent corrosionresistance in a wide variety of environments. Despite the commercialsuccess which the alloy has enjoyed, machinability of the alloy hasalways been limited and a high rate of tool wear has been encountered inmachining the alloy. Furthermore, diificulties have been encountered inwelding the alloy, particularly in respect to repair welding in thefield with the result that the alloy is not welded in commercial terms.In addition, the heat treatment which has been applied to the alloy hastraditionally been a very long heat treatment involving a furnace timeon the order of 28 hours or even more in order to develop high agehardened properties therein.

The machining problem, in particular, has been a vexing problem inconnection with the alloy and, despite many efforts, no commerciallyfeasible improvement in machinability has been discovered. For example,one expedient which has been found actually to improve machinability ofthe alloy to a marked extent has been an anneal at a high temperature,e.g., 2100 F. or higher. However, it was found that heat treatment at ahigh enough temperature to provide an improvement in machinability ofthe alloy resulted in production of extremely large grains, a conditionwhich could not be tolerated in commercial practice.

It is an object of the invention to provide an age hardenablenickel-copper alloy having improved machinability and weldability ascompared to alloys of the prior art.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawing in which is depicted a plot of cutting speed against tool lifeas established in machinability testing applied to the alloy of theinvention.

Broadly stated, the present invention comprises an age hardenablenickel-copper alloy containing not more than 0.10% carbon, e.g., about0.03% to about 0.10% carbon, not more than 0.5% titanium, e.g., about0.1% or about 0.2% to about 0.5% titanium, about 2.5 to about 3.5%aluminum, about 63% to about 70% nickel and the balice ance, with theexception of incidental elements and impurities, being essentiallycopper. A preferred alloy in accord ance with the invention nominallycontains about 0.07% carbon, about 0.3% titanium, about 3% aluminum,about 63% to about 70% nickel and the balance essentially copper.

In providing the alloy in accordance with the invention, the carboncontent is controlled within the range of about 0.03% to about 0.10%,and the titanium content is controlled so as not to exceed 0.5 to conferweldability and machinability to the alloy while at the same timeenabling the production of high strength therein upon aging. Thealuminum is maintained in the range of about 2.5 to about 3.5% to permitproduction of high properties upon aging the alloy. The alloy maycontain small amounts of incidental elements which do not materiallyaffect the basic and novel characteristics of the alloy including up toabout 2% iron, up to about 1.5% manganese, and up to about 0.5 silicon.In common with other nickel-base alloys, sulfur is an undesirableimpurity and should not exceed 0.010% while phosphorus should not exceedabout 0.02%. In the interests of preserving weldability, machinabilityand hot malleability in the alloy, the boron content should not exceed0.01%.

The alloy is age hardened by heating to a temperature in the range ofabout 1100 F. to about 1225" F. and then slowly cooling, e.g., at a rateof 25 F. per hour or less, the alloy to a temperature of about 900 F.Alternatively, the alloy can be held successively at temperatures ofabout 1150 F., 1050 F. and 950 F. for periods of up to about 8 hours ateach temperature and with furnace cooling between each step. The alloydisplays a maximum rate of hardening at about 1150 F. A preferredparticularly satisfactory heat treatment comprises a heating at about1150 F. for about 2 to about 8 hours, e.g., 2 hours, furnace cooling to1050 F., holding for about 2 to about 6 hours, e. g., 4 hours, furnacecooling to 950 F., holding for about 2 to about 6 hours, e.g., 4 hours,and then cooling. It is thus possible to age the alloy by means of atime cycle only a little over 10 hours in length. Longer aging cyclesimprove the mechanical properties only slightly, and it was surprisingto find that the short cycle heat treatment was so effective in agingthe alloy. Hot finished and aged, e.g., hot rolled and aged or forgedand aged products will provide a yield strength (0.2% offset) of atleast 80,000 pounds per square inch (p.s.i.), a tensile strength of atleast 130,000 psi. and an elongation of at least 20% measured over agage length four times the specimen diameter. Higher strengths areobtained in cold finished, aged material made from the alloy. In orderto develop maximum mechanical properties, the alloy is solution treatedor annealed at temperatures in the range of about 1350 F. to about 1400for times on the order of about /z hour, al though shorter annealingtimes, even as short as five minutes can be employed in the case of coldworked materials, e.g., rod, wire, strip, sheet, tubing, etc., with thehigher annealing temperatures. The low solution or annealing temperatureis a further important advantage of the alloy in that oxidation,distortion, grain growth and thermal shock effects are reduced oreliminated as compared to the case wherein higher annealing temperaturesare used. Higher annealing temperatures and shorter times, e.g., about1600 F. for one minute, can. be employed in special situations to annealout all prior work hardening and to provide material for deep drawing,spinning, flow turning, etc., operations which are usually performedupon thin strip or sheet material. It is not necessary to employ asolution treatment prior to aging; instead, worked material can bedirectly aged, usually with advantage in terms of higher mechanicalproperties in the aged material.

It is found that the alloy is immune to strainage cracking after weldingand, in addition, that the machinability of the alloy in all conditionsof working and heat treatment is excellent. The material produces along, stringy chip in machining and surface finish of machined pieces isexcellent. Horsepower requirements for cutting the alloy are about thesame as those for the known free machining stainless steel AISI Type 303(Se), i.e., about 0.7 to about 0.8 horsepower per cubic inch of metalremoved per minute. In general, best machinability is manifested whenthe alloy is machined in the annealed condition. This factor promotesthe desired practice in conjunction with age hardenable alloys ofmachining the alloy almost to finish size before hardening followed byfinished machining after hardening.

It is difficult to correlate machineability of an alloy with alloycomposition. However, intensive investigation of the machining problemhas resulted in development of a standardized testing techniqueutilizing an instrumented lathe and a single point tool of standardizeddesign. A series of test runs is made with a standardized depth of cutand a standard feed rate per revolution in cutting a round piece of thetest alloy. The cutting speed (measured in surface feet per minute) isvaried for each In order to give those skilled in the art a betterappreciation of the advantages of the invention, the following exampleis given:

A commercial scale electric arc furnace air melt was produced and castinto inch x 2.0 inch x 90 inch ingots. The alloy contained 65.37%nickel, 3% aluminum, 0.07% carbon, 0.84% iron, 0.54 manganese, 0.11%silicon, 0.30% titanium, 0.009% sulfur and the balance copper. One ingotwas hot rolled to a 4-inch diameter round without difliculty. A portionof the material was cold drawn to 3 /8 inch diameter rod while anotherportion was forged into a 2-inch square and a further portion wasfurther worked into the form of 4- inch diameter cold drawn rod. Theresulting: material was subjected toroom temperature tensile testing invarious conditions, including as-rolled, as-drawn, annealed and agedconditions with the results set forth in the following Table II in whichthe term annealed indicates a heat treatment at 1400 F. for /2 hour andthe term aged indicates a heat treatment comprising heating at 1150 F.for 2 hours, furnace cooling to 1050" F. and hold for 4 hours (2 hourswhere symbol (A) appears), furnace cooling to 950 F. and hold for 4hours followed by air cooling to room temperature.

TABLE II Y.S. (0.2% T.S., E1., R.A., Hard- Diameter size, inchesCondition ollset), p.s.i. p.s.i. percent percent ness in area.

run and the tool life in minutes to develop a 0.015 inch wearland on thetool point in the case of carbide tools and a 0.050 inch wearland on thetool point in the case of high speed steel tools was measured on eachrun. The resulting data are plotted to develop curves such as thoseillustrated in the drawing. Good machinability is indicated by theplotted data when the resulting lines are straight and follow a uniformpath. Erratic tendencies revealed by the plotted data and lack ofstraightness in the lines is in indication of poor machinability. Highordinate values for the plotted data constitute a further indication ofgood machinability. In order to reduce variables, most of the testingwas done using carbide tools. Sufficient testing was done with highspeed steel tools to indicate similar trends to the results obtainedusing carbide tools. The results can be compared by a machinabilityindex based on 30-minute tool life (V in accordance with the relation:

condition tested (V X 100 standard condition (V Using the hot rolled,annealed (1400 F. /2 hour) condition as standard, the comparisons areshown in the following Table I:

Machinability index Fatigue testing on annealed and aged material fromthe 2-inch square forging as determined by the rotating bend fatiguetest demonstrated a life at 10 cycles of 46,200 p.s.i. reversed stressand a life at 10 cycles of 43,500 p.s.i. reversed stress.

Material from the heat in various conditions was subjected to amachining test using single point carbide tools with the resultsillustrated in the drawing. The tool material employed was atungsten-titanium carbide material with a cobalt binder. The tool wascut with a back rake angle of 0, a side rake angle of 5, an endclearance angle of 5, a side clearance angle of 5, an end cutting edgeangle of 15, a side cutting edge angle of 15 and a nose radius of inch.The cutting site was flooded with a commercial coolant. A feed rate of0.00825 inch per revolution with a depth of cut of 0.050 inch wasemployed in the test. A tool life end point was taken as 0.015 inchflank wear. Excellent surface finish was observed in the testing. Asillustrated in the drawing, the machinability data was plotted inuniform straight lines and no tendency toward erratic behavior wasobserved. In addition, the ordinate values (cutting speed velocity) arevery high, further indicating excellent machinability. The millcondition, e.g., hot rolled and annealed, in which the alloy wassubjected to the machinability test is indicated on the tool life linesin the drawmg.

Weldability of the material was demonstrated by means of restrained buttwelds made on l-inch thick forged flats in the age hardened conditionresulting from an anneal at 1400 F. for /2 hour, air cooled and aged at1150 F. for 2 hours, furnace cooled to 1050" F., hold 4 hours, furnacecooled to 950 F., hold for 4 hours and air cool. The aged flats werebutted together with a V- groove therebetween and welded to a 4-inchthick steel strongback. The V-groove was then completely filled with astandard nickel-copper covered Welding electrode. The entire assemblywas then given a further aging treatment as described hereinbefore. Thewelded nickel-copper alloy assembly was then cut from the strongback andthe weld was sliced for examination. No strainage or underbed crackingwas observed and side bend tests in which Aa-inch thick transverseslices cut through the weld were bent about a 1 /2 inch diameter pinindicated there were no fissures or voids in the weld area. The tensileproperties of the aged weld material were determined by means oftransverse tensile tests produced from tensile specimens, including theweld, together with all weld metal tests. The results are set forth inthe following Table III:

TABLE III Y.S. (0.2% T.S., EL, Location of Test oflset), p.s.i. p.s.i.percent fracture Transverse 95,500 138, 500 22. Parent metal.

D0 93, 500 137, 500 22. 0 DO. Longitudinal all 112, 000 150, 000 7. 0Weld.

weld metal.

Do 109, 500 148, 000 17. 0 Do.

very low level of machinability. Thus, the machinability level withcarbide tools was lower than that of high speed steel tools. Again, aheat of 0.15% carbon, 0.54% titanium, with essentially no other changein composition from the alloy described in the example, indicated verypoor to no machinability. Thus, the tool life line had a reverse curveat a very low machinability level indicating a highly undesirablecondition as shown by Curve A in the drawing for cold drawn, as-drawnmaterial made of the alloy. Curve B in the drawing is the tool life linefor cold drawn, aged material made of this alloy outside of theinvention.

The alloy provided in accordance with the invention is characterized byhigh strength, toughness and ductility over a wide range of temperaturesand is useful over the temperature range from minus 423 F. to about 800F. The alloy may be fabricated into such articles as pump shafts andimpellers, propellor shafts, oil well drill c01- lars and instruments,doctor blades and scrapers, valve trim, springs, etc. The alloy isreadily produced in any of the common mill forms, including rod, bar,sheet, strip, tubing, extruded shapes, forgings, etc.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. An age hardenable alloy having improved machinability and weldabilityin wrought form consisting essentially of about 63% to about nickel,about 2.5% to about 3.5% aluminum, about 0.07% carbon, about 0.3%titanium, not more than about 2% iron, not more than about 1.5%manganese, not more than about 0.5% silicon, not more than about 0.010%sulfur and the balance essentially copper.

2. In the production of wrought age hardenable nickelcopper alloyscontaining aluminum and titanium as age hardening ingredients, theimprovement in compositional control therefor to provide enhancedmachinability and freedom from weld cracking while retaining highstrength in the aged condition which comprises controlling the carboncontent in the range of about 0.07% the titanium content in the range ofabout 0.3% the aluminum content in the range of about 2.5% to about3.5%, the nickel content in the range of about 63% to about 70% and withthe balance essentially copper.

3. The process for age hardening an alloy consisting essentially ofabout 63% to about 7 0% nickel, about 2.5 to about 3.5% aluminum, about0.03% to about 0.10% carbon, about 0.1% to about 0.5% titanium, and thebalance essentially copper which comprises heating the alloy at atemperature of about 1150 F. for about 2 to about 8 hours, furnacecooling to about 1050 F., holding at about 1050 F. for about 2 to about6 hours, furnace cooling to about 950 F., and holding at about 950 F.for about 2 to about 6 hours.

4. The process according to claim 3 wherein the alloy is annealed, priorto aging, at a temperature not exceeding about 1400 F.

5. The process according to claim 3 wherein the alloy is held at about1150 F. for about 2 hours, at about 1050 F. for about 2 to about 4hours, and at about 950 F. for about 4 hours.

References Cited UNITED STATES PATENTS 3/1939 Bieber -170 3/1941 Bieberet al. 75-170 US. Cl. X.R. l4812.7, 162

